Field of the Invention
The present invention concerns a method, a magnetic resonance apparatus, and also a non-transitory, computer-readable data storage medium for determining a measurement variable that is relevant to a function of an organ of a patient.
Description of the Prior Art
To determine a function of an organ, i.e. an organ function, blood examinations will frequently be carried out. For example the function of a liver can be obtained by blood tests before and after the injection of Indocyanine green (ICG). In this way a determination of the absolute liver function, a prediction of the post-operative liver function and/or a monitoring of the function increase after portal vein embolization can take place. ICG examinations are deemed to be the gold standard for determining the liver function.
In magnetic resonance imaging, the body of a person (patient) to be examined by a magnetic resonance scanner is usually subjected by a basic field magnet to a relatively high basic magnetic field, for example of 1.5 or 3 or 7 Tesla. In addition, gradient fields are activated by a gradient coil arrangement. Then radio-frequency pulses, for example excitation pulses, are radiated by a radio-frequency antenna unit by means of suitable antenna elements, which leads to the nuclear spin of specific atoms, which are resonantly excited by this radio-frequency pulse, being flipped by a defined flip angle in relation to the magnetic field lines of the basic magnetic field. During the relaxation of the nuclear spins, radio-frequency signals, called magnetic resonance signals, are emitted, which are received by suitable radio-frequency antennas and then further processed. Finally the desired image data can be reconstructed from the raw data acquired in this way.
Therefore, a specific magnetic resonance sequence is activated for a specific measurement, the sequence including a series of radio-frequency pulses, for example excitation pulses and refocusing pulses, as well as gradient switchings suitably coordinated thereto along different gradient axes in different spatial directions. Time-matched readout windows are activated, which specify the periods of time in which the induced magnetic resonance signals will be acquired.
The image data are spatially resolved and represent the reconstructed magnetic resonance signals. Depending on the magnetic resonance sequence used and also on the reconstruction method, the image data can have different contrasts and can reflect the anatomy or also specify different quantitative values.
In magnetic resonance imaging, depending on the clinical problem, a contrast medium may be administered to the patient. Contrast media, for example, can circulate in the blood stream or can attach to specific molecules or cells and can accumulate at those sites. At the places at which the contrast medium accumulates, the contrast medium changes the contrast of the image data and/or changes the quantitative values specified in the image data, compared to a recording without a contrast medium, in particular during use of an otherwise identical magnetic resonance sequence and reconstruction method. The accumulation of a contrast medium depends on the type of contrast medium. For example, contrast media are known that will be taken up and passed on by specific cell types. The concentration of such cell types accordingly is correlated with the concentration of the corresponding contrast medium. The concentration of a contrast medium is typically determined specifically for one contrast medium.
A clinical study (Haimerl et al., “Volume-assisted estimation of liver function based on Gd-EOB-DTPA—enhanced MR relaxometry”, doi 10.1007/s00330-015-3919-5, Eur Radiol) has shown that magnetic resonance imaging using hepatocyte-specific contrast media, e.g. Primovist, Eovist, delivers comparable results to ICG examinations. In this case, the concentration of the hepatocyte-specific contrast medium correlates with the concentration of the healthy liver cells. The determination of the concentration of the hepatocyte-specific contrast medium is based on a measurement of the relaxation time T1.